This invention relates to baseband signal switching arrangements for diversity reception in a pulse-modulated microwave communication system.
Generally, in a radio communications system, diversity reception technique is employed to enhance the reliability by minimizing the effects of fading with selection of signals received through two or more radio wave propagation paths provided therefor. As is well known, the diversity reception system takes a number of forms, including a space diversity reception which utilizes transmission through a plurality of propagation paths by employing receiving antennas placed in different locations and a frequency deversity reception which utilizes transmission through a plurality of propagation paths by using different carrier wave frequencies. One example of the space diversity reception system is described in a publication, the "IEEE Transactions on Communications Technology," Vol. 15, No. 4, Aug. 1967, pp. 603.about.614. The selection of the signals received through the propagation paths is effected in either the intermediate frequency band stage or the baseband stage of the diversity receiver. In such a system, those signals propagated through the fading-affected propagation paths are disconnected while the unaffected signal is led to the receiver output. When one of the propagation paths is switched to the other paths, an instantaneous signal interruption is inevitably caused at the receiver output. Such signal interruption has no appreciably adverse effects upon the signal being received as far as analog signal communications are concerned. In the case of the digital signal transmission, however the instantaneous signal interruption causes not only the collapse of the synchronized state of the system as a whole but also the loss of information being transmitted. Furthermore, it gives rise to bit errors in its output. Under the situation, there is an increasing demand for a switching device capable of selecting the favorable propagation path without causing any instantaneous signal interruption and thus without resulting bit errors in its output.